[M]ost of the Kleiner’s green-tech investments are not publicly
discussed. By my count, the firm has acknowledged 15 of its 40
investments. The rest are in what V.C.’s call “stealth” mode,
hidden from the press (and copycat V.C.’s) until they are on
sounder footing.

Last summer, the growing number of stealth companies involved
with clean energy formed a kind of dark matter in the Silicon
Valley universe, businesses that could not be seen yet
nevertheless exerted a discernible gravitational pull. Executives
would suddenly leave jobs at established companies to join
ventures with no official name. Manufacturing facilities would
set up shop in cheap, anonymous buildings in towns like Santa
Clara, Calif., then begin round-the-clock operations.

When Kleiner decided to invest in a company called FloDesign, a
business in Massachusetts, sensitive pages on its Web site were
quickly dismantled; when Kleiner decided to invest in a company
known as Sundrop Fuels, online links that described the
technology, which was developed at Los
Alamos National Laboratory, were removed. In some respects,
the more promising the technology, the more secretive the venture
becomes. And both FloDesign and Sundrop were indeed promising.

FloDesign intends to replace the common propeller wind turbine
with something that resembles a jet engine. Doerr told me that
the company’s product, which is perhaps 18 months away from a
prototype, would cost 25 percent less than any other kind of wind
generation — that could make it one of the cheapest
renewable-energy sources in the world. Sundrop, meanwhile, is
what Joe Lacob, a Kleiner partner, calls “solar assisted” fuel
generation — a process that combines the ingredients of carbon,
hydrogen and sunlight to create a petrol-like product. “We can
actually take CO2,” Lacob told me, “which is what we’re trying to
get rid of, and make that our source of carbon, and use the sun’s
energy to create liquid fuels.”